Materials recycling apparatus

Abstract

Materials recycling processes that include a combustion stage can operate very efficiently, but can produce exhaust gases that are high in carbon monoxide and the like. We describe a treatment unit which comprises a chamber for receiving the material, a heat source for (preferably) heat-treating the material and for initiating combustion, and a gas outlet from the chamber, which allows the gas that is exhausted via the outlet to be supplied to the air inlet of an associated boiler unit, with the air inlet and a separate fuel inlet feeding a burner for combusting fuel from the fuel inlet in air from the air inlet in order to heat a transfer fluid. In this way, the unburnt elements of the gas expelled from the chamber are included in the combustion process of the boiler unit and fully combusted. A corresponding method is also disclosed.

Claims

1. A method of treating material, comprising the steps of: heat-treating the material anaerobically to yield pyrolysis products namely syngas and oils; extracting the pyrolysis products to leave behind a char residue; admitting oxygen thereby to combust the char residue in the absence of the pyrolysis products; exhausting at least the gaseous combustion products from the combustion of the char residue to a boiler unit, optionally admixing these combustion products with air; in the boiler unit, combusting a fuel in combination with the gaseous combustion products, to heat a transfer fluid.

2. A method according to claim 1 in which the gaseous combustion products are fed to the boiler unit via a heat exchanger.

3. A method according to claim 1 in which the gaseous combustion products are fed to the boiler unit via a scrubber to remove entrained particulates.

4. A method according to claim 1 in which the transfer fluid is water-based.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the present invention will now be described by way of example, with reference to the accompanying FIGURES in which the sole FIG. 1 schematically illustrates an arrangement according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(2) FIG. 1 shows a schematic layout of the overall system. Resource materials for recycling are loaded into a treatment chamber 10 where they are anaerobically heated to around 300-400 C. at which the material is pyrolised, yielding a range of products including mainly syngas and oils. Once pyrolysis is complete, these are removed via an outlet 12 and stored in a buffer 14. This leaves behind a residue which can be combusted by opening a valve 16 to allow a supply of air into the treatment chamber 10 while still at an elevated temperature. The hot exhaust gases from the combustion process can then be vented via an exhaust valve 18 to a heat exchanger 20 where the residual heat can be transferred to the transfer fluid of a conventional hot water system (explained more fully below). The cooled exhaust gases are then passed through a scrubber 22 to remove ash and other particulates; this is described and claimed in our copending application no. GB1706489.0 filed on 24 Apr. 2017 to which the reader is referred for a fuller description.

(3) The exhaust gases are then pumped by pump 24 into a temporary store 26, and held there by closing valves 28, 30 on either side. When the boiler 32 is next activated, valve 30 can be opened to allow the exhaust gases to leave the temporary store 26 and be mixed with the air inlet 34 to the boiler 32. A non-return valve 36 should be provided in the air inlet 34 to prevent gases from the temporary store 26 from escaping to the atmosphere. In alternative arrangements, the exhaust gases can be mixed with a gaseous fuel such as LPG or natural gas supplied to the boiler via its gas inlet pipe, or they can be introduced directly into the burner of the boiler via a separate injection means. However, admixing the exhaust gases with the air supply is particularly convenient.

(4) Storage of the exhaust gases in the temporary store is useful in that the combi boiler does not then need to be running continuously for the entire period during which the treatment chamber 10 is operating or combusting. This is possible (in which case the temporary store 26 could be omitted) but would not be efficient. In practice, the exhaust from the treatment chamber 10 produces about 0.03 cubic metres per second; when run through a small compressor 24 and put in a 20 litre capacity tank at (for example) 4 bar this allows approximately 81 litres of storage or 5 minutes of operation of the treatment chamber 10. A typical combi boiler takes 0.25 cubic metres per second, so will require only 30 seconds of running to consume the output of the previous 5 minutes. The boiler is therefore operating at a mark/space ratio of 1:10, significantly more efficient.

(5) During this time, the output of the boiler can be used for space heating or for hot water generation and so use is made of the heat. Of course, the capacity and pressure of the temporary store 26 could be varied so that the exhaust gases are retained until such time as there is a heating or hot water demand and then released in their entirety.

(6) The boiler 32 is a conventional domestic boiler, in this example. It receives a supply of natural gas from a gas inlet pipe 38 and burns this in air supplied via the air inlet 34. Exhaust gases are vented to the atmosphere via a flue 40. The heat that is generated is transferred into a transfer fluid, usually water containing corrosion inhibitors and the like. This circulates around a heating system via pipework 42; as is conventional this system include (i) a hot water tank 44 within which a heat exchanger 46 fed with the transfer fluid by the pipework 42 transfers the heat into clean water 48 that can then be used for sanitary purposes, and (ii) a plurality of radiators 50 which are fed with the transfer fluid and radiate heat from the fluid into the rooms in which they are located. A circulation pump 52 urges the transfer fluid around the pipework when needed, and ensures that the fluid does not dwell in the boiler where it might overheat and cavitate. Valves are usually provided so as to direct transfer fluid to the hot water tank 44 or the radiators, or both, as required, together with a control system to control activation of the boiler, the pump and the various valves. These are commonplace in the art and are therefore not illustrated and need not be described in detail.

(7) The exact details of the plumbing of the heating system are not essential to the present invention. For example, other types of heating system exist, for example systems in which the boiler is activated on demand in order to heat sanitary water directly, systems that deal with heating only, or hot water only, or which have more or fewer elements. The specific layout illustrated in FIG. 1 is by way of an example only and may be varied as necessary as is well known in the plumbing art.

(8) FIG. 1 also shows a link 54 from the pipework system 42 to the heat exchanger 20. A valve 56 between the link 54 and the pipework system 42 isolates the heat exchanger when necessary, and can be used to prevent heat generated by the boiler 32 (when active) from being dissipated in heating the heat exchanger 20. The valve 56 is opened when the exhaust gases from the treatment chamber 10 are being exhausted via the heat exchanger, to heat the transfer fluid. This can then be pumped around the pipework system 42 by the pump 52, either to heat the radiators 50 or to warm the water 48 in the hot water tank 44. Accordingly, efficient use is made of the heat employed to treat the material in the treatment chamber 10.

(9) In an experimental arrangement in which exhaust gases from a treatment chamber 10 were fed (diluted) into the air inlet of a conventional domestic boiler, the change in the gas content was observed to be:

(10) TABLE-US-00001 Constituent Chamber exhaust Boiler Flue O.sub.2 (%) 0.73 5.37 CO (ppm) 331 36.7 NOx (ppm) 50.4 14.1 NO (ppm) 48.0 13.4 CO.sub.2 (%) 13.29 9.95

(11) The exhaust gases were also observed to have lost a distinctive odour after passage through the boiler. Accordingly, the treatment of the exhaust gases in this manner converts an exhaust stream containing high pollutant levels into one that is considered safe to release into the atmosphere.

(12) As mentioned above, syngas and oils are released from the material being processed during pyrolysis and are extracted and stored in vessel 14. These may be fed via a suitable pump and pipework (not shown) to the fuel inlet 38 of the boiler 32, further increasing the efficiency of the system by reducing the fuel demands of the system. The CO content of the gas provided to the boiler will also release some heat on combustion to CO.sub.2, meaning that the overall system provides a safe and effective means for recycling resources, yielding a non-odorous output that is safe to vent, and incidentally reducing the fossil fuel demand of the boiler.

(13) It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.